Fig. 3.

Drop dynamics. (A) Scaled rotational velocities $u_{\perp }/V_0$ for silicone oil drops ($\mathrm{\Omega }=2\mathrm{to}6{\text{mm}}^3$, $\mu =10\mathrm{to}101$ mPa-s). The transition from groove flow to either skipping or barrel flow is delineated by the dimensionless length ${\mathrm{\Omega }}^{1/3}/\lambda$. (B) Center of mass trajectory plots in the $y$-$z$ plane for a silicone oil drop in either groove or skipping flow. For groove flow, the center of mass oscillates with a single wavelength $2\lambda$. For skipping flow, the drop’s center of mass oscillates into and away from the fiber as it skips over the fiber’s twisted structure, causing a short wavelength oscillation set by $\lambda$ superimposed onto a longer wavelength oscillation set by $u_{\perp }$ and $u_{||}$. (C) The drop’s center of mass position against time $t$. During skipping flow, the drop may spontaneously transition into barrel flow. Its downward velocity $u_{||}$ decreases due to the additional wetted area and its center-of-mass moves toward the fiber $\widehat{x}=\widehat{y}=0$. Only transitions away from skipping flow are observed.